Method and apparatus for counting work cycles of electrically driven devices

ABSTRACT

An accurate count of the number of workpieces processed on an electrically driven machine tool is maintained by a counter controlled by a circuit which responds to the changes of drive motor current in the course of each work cycle. As the counting system is not dependent upon detection of any mechanical movement, critical elements of the system may be inaccessibly located to avoid possible tampering with the count. The system can be adapted to counting work operations which involve more than one motor current peak in connection with processing of a single workpiece and is insensitive to supply current fluctuations arising from other causes such as motor starting surges and the like.

United States Patent 1 Isnard [451 Feb. 19, 1974 METHOD AND APPARATUS FOR COUNTING WORK CYCLES OF ELECTRICALLY DRIVEN DEVICES Theophile Isnard, Pont de Claix, France Caterpillar Tractor Co., Peoria, [11.

Dec. 23, 197

Inventor:

Assignee:

Filed:

Appl. No.:

Foreign Application Priority Data Feb. 17, 1971 France 71.05427 235/92 FP, 235/92 PD US. Cl. 235/92 EL, 235/92 R,

Field of Search ..235/92 PD, 92 EL, 92 FQ,

[56] References Cited UNITED STATES PATENTS 7/1967 McCauley 235/92 R 10/1967 Allured 235/92 PD .Int. Cl. 606m l/27 235/92 c 92 EC, 92 FP Stiebel 235/92 PD Strieby 235/92 EL Primary ExaminerMaynard R. Wilbur Assistant ExaminerRobert F. Gnuse Attorney, Agent, or Firm Fryer, Tjensvold, Phillips & Lempio [5 7 ABSTRACT An accurate count of the number of workpieces processed on an electrically driven machine tool is maintained by a counter controlled by a circuit which responds to the changes of drive motor current in the course of each work cycle. As the counting system is not dependent upon detection of any mechanical t.mq stnsnsgfi salslsm nis cithwz x be accessibly located to avoid possible tampering with the count. The system can be adapted to counting work operations which involve more than one motor current peak in connection with processing of a single.

workpiece and is insensitive to supply current fluctuations arising from other causes such as motor starting surges and the like.

9 Claims, 3 Drawing Figures i 3 PHASE AC. 33- /I\ Z4\ 7 POWER SUPPLY i g 1 O METHOD AND APPARATUS FOR COUNTING WORK CYCLES OF ELECTRICALLY DRIVEN DEVICES BACKGROUND OF THE INVENTION This invention relates to the counting of work cycles of an electrically driven device and more particularly to a method and apparatus for electrically counting work cycles at a machine tool or the like in a highly reliable and tamper-proof manner.

In production operations at powered machine tools or other electrically driven systems, it is often desirable to maintain an accurate count of work cycles of the system or of the number of workpieces turned out on the tool. This may be desirable, for example, in the course of time and motion studies or in situations where operators are compensated on the basis of quantity of production. Counting devices heretofore employed for this purpose have involved various means for sensing some mechanical movement at the tool or the like which occurs in the course of each work cycle. Such devices are inherently susceptible to tampering or manipulation whereby false counts may be recorded. Moreover, such devices may be complex and bulky, prone to wear and difficult to install on certain machines.

SUMMARY OF THE INVENTION This invention is a method and apparatus for counting work cycles in an electrically driven system which is less susceptible to tamperingand which may utilize compact economical elements. These results are accumplished by sensing and counting changes of electrical current to the drive motor or the like which occur in the course of each work cycle. An electrical motor, for example, typically draws an increased current each time it is loaded to perform a work operation. In a preferred form, means are provided for discriminating against current fluctuations which arise from other causes, such as the current surges associated with initial starting of a motor, and the system is adaptable to work cycles which may involve a series of current variations in the course of a single cycle.

Accordingly it is an object of this invention to facilitate the obtaining of reliable counts of work cycles performed by an electrically driven device.

It is another object of this invention to provide a method and apparatus for maintaining a count of workpieces turned out on a machine tool or the like which is less susceptible to tampering and which may be compact, economical and durable.v

The invention together with further objects and advantages thereof will best be understood by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an elevation view of an inertia welding machine showing elements of a work cycle counting system associated therewith,

FIG. 2 is a circuit diagram showing electrical elements of the work cycle counting system of FIG. 1, and

FIG. 3 is a circuit diagram showing a modified circuit for use where multiple current peaks may occur in the course of a single work cycle.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawings, an inertia welding machine 11 is shown in order to illustrate how the circuit of the present invention may be coupled to a typical machine tool at which a count of work cycles is to be maintained. It will be apparent that the circuit is equally applicable to other forms of machine tool as well as other electrically driven apparatus which would not normally be characterized as a machine tool. Inasmuch as the structure and operation of an inertia welder 11 is known, only those elements of the welder which are necessary to understand the coaction of the present invention therewith will be herein described.

Welder 11 may have a base 12 supporting a rotatable spindle 13 which carries a flywheel l4 and a rotary chuck 16, the spindle, flywheel and rotary chuck being driven by an electrical motor 17 which is of the threephase alternating current form in this example. Slidably positioned on base 12 opposite the rotary chuck 16 is a tailstock 15 carrying a non-rotating chuck 18. Tailstock 15 and chuck 18 may bemoved towards the rotary chuck 16 and away therefrom by suitable means such as a hydraulic cylinder 21 within base 12. The drive motor 17 is coupled to a suitable three-phase alternating current power supply 22 through three conductors 23, 24 and 26 and a switch 27 for selectively energizing the motor.

In order to weld workpieces, which in this example are formed from two short rod-like elements 28A and 288, one such element 28A is mounted in the rotary chuck 16 and the other is similarly mounted in the chuck 18 is coaxial relation to the first element. Motor 17 is then energized by closing the switch 27 which then accelerates spindle l3, flywheel 14, rotary chuck 16 and element 28A to a high angular velocity with the result that substantial kinetic energy is stored in the several rotating elements. Motor 17 is then deenergized by opening switch 27 although in some other forms of inertia welder the motor remains energized and clutch means are provided to decouple spindle 13 from the motor. In either case, the spindle 13, flywheel l4, rotary chuck 16 and element 28A continue to rotate owing to the kinetic energy stored therein. Hydraulic cylinder 21 is then actuated to shift the element 283 into abutment with rotating element 28A. Friction at the resultant contacting ends of elements 28A and 288 then acts to rapidly brake the rotating elements with the kinetic energy of rotation being converted into intense heat at the zone of contact of the two elements. This heats the contacting ends of elements 28A and 283 to a plastic condition so that when the rotating elements come to rest, the two elements are fused together. Tailstock assembly 15 may then be retracted and the welded workpiece formed of elements 28A and 28B is removed.

Of interest relative to the present invention is the fact that the current drawn by motor 17 from power supply 22 is a function of the load on the motor and thus rises during the period that the spindle l3, flywheel l4, and other rotating elements are in the process of being accelerated. As is well known in the electrical motor art, there may also be a relatively brief but high amplitude current spike at the time motor control switch 27 is first closed as the motor offers very little impedance to current flow until such time as substantial armature speed has been brought about. In instances where a clutch is employed to decouple: the motor 17 from the spindle 13, without deenergizing the motor, there is stilla rise of motor current during the period that the motor is accelerating the flywheel l4 and associated elements inasmuch as the current drawn by a motor is a function of the load. 7

Essentially a similar situation occurs in many other forms of electrically driven tools, other than the inertia welder herein shown for purposes of example. In. lathes, drill presses, milling machines and diverse other apparatus, an electrical motor draws a varying amount of current from the power supply in a predictable manto each such. current change. In the present example,

the counter 29 is a visually readable type mounted on the cabinet 32 of the welder 11 which contains other electrical control elements of the welder. The circuit 31 which drives the counter is within the closed cabinet 32 where it is relatively inaccessible to the operator. In some instances the circuit 31 may be situated remote from the welder 11 as it operates wholly through electrical connections to the conductors 23, 24 and 26 which supply electrical current to the motor and these conductors'may extend a considerable distance away from the welder.

Operating power for the counter circuit 31 is obtained through conductors 33 and 34 which connect to two of the motor supply current conductors 26 and 24 respectively. In order that the circuit 31 remainenergized when the motor control switch 27 is open, this connection is preferably made between that portion of the conductors 26 and 24 which extendbetween switch 27 and power supply 22. To provide a means for detecting current changes in the motor conductors, a pair of conductors 36 extend from the circuit 31 and are connected to the secondary of a current sensing trans former 35 having the third motor power supply lead 23 as a primary.

Considering now a suitable detailed configuration for the counter circuit 31, reference should be made initially to FIG. 2. The two conductors 36 connect to opposite ends of the primary coil of an adjustable transformer 37. The secondary winding of transformer 37 is in turn connected across the input terminals of a full wave diode bridge rectifier 38. One output terminal of rectifier 38 connects to a terminal 39 through a resistor 41 while the other output terminal of the rectifier connects directly with a terminal 42. Thus a DC voltage E-1 appears between terminals 39 and 42 and has a magnitude proportional to the current in motor power supply conductor 23. To filter out the ripple which might otherwise be present in the output of a bridge rectifier 38 of this form, a capacitor 43 and resistor 44 are connected across the output terminals of the rectifier. To limit the maximum voltage differential between terminals 39 and .42, a zener diode 46 is also connected across the output of the rectifier.

Accordingly, when the load on motor 17 increases in the course of a work cycle, the resulting increase of alternating current in motor conductor 23 inductively increases the amplitude of the alternating current at the output of transformer 37. DC voltage E-l therefore increases inmagnitude at'that time/Anadditional capac itor 47 isconnected betweeniterminals39 truth .to that the voltage E 1 does not rise abruptly when the currentdrawn by motor 17 increases, the delay intlie rise of the voltagebeing determined primarily by the time constant of the R 0 network defined by resistor 41 and capacitor 47. This avoids anyipronounce d increase of voltageB-l in response to very: brief current surges such as may occur as motor 17 isfirst energized or'froin:

other causes;

While the above described means protect against an erroneous workdcycle signaha'rising from very brief motor curreritincreases, it is also desirable to'discriminate against current changeswhicha'rise from variations in the voltage of the'power. supplied to motor 17.

Accordingly, voltage E4; is continually compared with a second voltage E-2 derived from the motor power supply conductors and' a work cycle count is initiated only when a rise of voltage E-l is unaccompanied by a corresponding rise of voltage E 2. To obtain the comparison voltage E 2, theprimary winding of asecond adjuatable transformer 48 is connected between the previously described power conductors. 33 and 34 former 48is connected across the input terminals of a second full wave diode bridge rectifier 49. A potentiometer 51 and resistor '52 are connected in series the capacitor 63 and resistor 64 differentiate the de across the output terminals of rectifier 49 and a ripple V smoothing capacitor 53 is also connected across the output terminals in parallel relationship with the potentiometer and resistor. The movable contact of potentiometer 51 isconnected to a ground conductor 54 and the negative output terminals of both rectifiers 38" and 49 are connected to terminal 42. Thus a DC voltage E-2 is present between the terminal 42 and ground conductor 54 and varies as a function of anyvoltage changes in the power supply leads to motor 17. Voltage .E-2 thusconstitutes a reference voltage against which voltage E-l may be compared to detect increased current to motor 17 as a result of loading of the motor as distinguished from current increases due to fluctuations of the motor power supply voltage. As'voltage E-l appears between'terminals 39 and 42 while voltage E-2 appears between ground conductors 54 and terminal 42, a difference voltage-E-3 is present between ter minal 39 and the ground conductor. To limit this difference voltage E-3 to a predetermined magnitude, a zener diode 56 and a protective capacitor 57 are connected between terminal 39 and ground conductor 54.

When motor 17 is not loaded, difference voltageE3- remains essentially constant at the value determined by zener diode 56. When voltage E-1 rises due to motor loading, voltage E-3 decreases and this decrease is caused to initiate a work cycle count. For this purpose, input conductors 58 and 59 of an amplifier 61 are connected to ground conductor 54 and terminal 39 respectively through a differentator circuit 62. In particular, amplifier input 59 connects to terminal 39 through a capacitor 63 while amplifier input 58 connects directly with ground conductor 54 and a resistor 64 is connected across the amplifier input conductors whereby crease of voltage E.3 accompanying a work cycle and apply the differentiated signal to the amplifier input. Amplifier 61 in turn, applies an amplified signal tothe input 66 of aSchmitt trigger circuit 67.

DC operating voltage for both the amplifier 61 and Scmitt triger 67 is obtained through a third transformer 68 having a primary winding connecting to the previously described conductors 33 and 34 respectively and having a secondary winding connected across the input terminals of a third full wave diode bridge rectifier 69. The negative output terminal of rectifier 69 is grounded while the positive output terminal connects with a power terminal 71 for the Schmitt trigger circuit 67 and amplifier 61. To smooth ripple from the output of rectifier 69 a capacitor 70 is connected between the positive output terminal and ground.

The collector of transistor 72 of the amplifier 61 connects with power terminal 71 through a resistor 73 and an additional resistor 74 of the Schmitt trigger. In addition to the transistor 72, amplifier 61 may consist of a resistor 77 connecting the base of the transistor with amplifier input 59 and a resistor 78 connecting the transistor emitter with grounded input 58. A protective diode 79 is connected between the transistor emitter and input 59 and a capacitor 81 is connected between the collector and ground to suppress transient voltage spikes.

When voltage E-3 decreases due to an increased motor current, differentiator 62 applies a momentary voltage to the base of transistor 72 through base resistor 77 causing the transistor to conduct. The input 66 of Schmitt trigger 67 is connected to the collector of transistor 72 and thus the momentary conduction of the transistor causes a momentary voltage decrease at input 66.

Schmitt trigger 67 may consist of a transistor 82 having a base connected to input 66 through a resistor 83 and having a collector connected to the power supply terminal 71 through a resistor 85 and resistor 74. A zener diode 84 is connected between the emitter of transistor 82 and ground and diode 86 is connected between the emitter and-base of the transistor. Accordingly transistor 82 is normally conductive and becomes non-conductive when the previously described momentary voltage drop is applied to the base through input 66. To assure that a predetermined constant operating voltage is applied to the collector of transistor 82, another zener diode 87 is connected between power supply terminal 71 and ground through resistor 74. Zener diode 87 also has the effect of providing a constant operating voltage to amplifier 61. A capacitor 88 connected between the base of transistor 82 and ground avoids stopping of conduction through the transistor in response to brief spurious voltage transients.

Schmitt trigger 67 further includes a second transistor 89 having a base connected to the collector of transistor 82 and having an emitter connected to the emitter of transistor 82 and thus to ground through zener diode 84. The collector of transistor 89 connects to power supply terminal 71 through a relay driver coil 91 and also through a diode 92 which protects the transis tor against transient voltages arising from the collapse of the magnetic field of coil 91.

Thus transistor 89 is nonconductive as long as transistor 82 is in conduction. While transistor 82 ceases to conduct in response to a signal at input 66 a positive voltage rise occurs at the base of transistor 89 which then conducts to energize coil 91.

Energization of coil 91 closes normally open relay contacts 93. Relay contacts 93 are connected between one input of counter 29 and power conductor 34 in se- 6 ries with a load resistor 94, the other input of the counter being connected directly to power conductor 33. Accordingly each momentary closing of contacts 93 initiated by the current increase at motor 17 applies one pulse count to counter 29 which displays the total of pulse counts received and thus visually indicates the number of work cycles which have been performed by motor 17.

The above described circuit configuration is readily adjustable to accommodate'to specific conditions at the particular machine tool with which the motor 17 is associated. The magnitude of the voltage E-l and the magnitude of the reference voltage E-2 may be selected to provide sensitivity to the major current change accompanying a work cycle, while discriminating against minor current changes by appropriate adjustments of the variable transformers 37 and 48 and potentiometer 51. Once these adjustments are made to accommodate to the specific tool, further changes are unnecessary. Of particular significance with respect to forestalling tampering'and attempts to register false counts is the fact that the entire circuit 31 need connect only to the power leads to the motor 17. These connections are readily made inaccessible.

The form of the circuit described above with refer ence to FIG. 2 was designed for use with a machine tool or the like wherein there is a single substantial current increase with each work cycle to be counted. In some instances, a machine tool may exhibit several current increaseof more or less similar magnitude in the course of a single work operation. FIG. 3 illustrates a modified form of the circuit in which the counter 29 will record a single additional count for each work cycle of a machine of this kind wherein several current increases may occur during the work cycle.

As in the previously described embodiment of the invention, the circuit 31' of FIG. 3 includes power supply conductors 33 and 34 which connect to two of the three conductors 26 and 24 respectively between motor power supply 22 and the three-phase motor 17 and further includes a current sensing transformer 35' having the third motor current conductor 23 as a primary, no other connections to the motor and power supply being necessarily required. Certain portions of the modified circuit 31' of FIG. 3 are essentialy similar to corresponding portions of the previously described circuit and accordingly will not be redescribed in detail, the elements of these unmodified portions of the circuit being identified in FIG. 3 by primed reference numerals corresponding to the reference numerals used in FIG. 2 for similar elements. These essentially unmodified portions of the circuit of FIG. 3 include a transformer 68 and rectifier 69' coupled to conductors 33 and 34 to provide DC operating power at a terminal 71 and an additional transformer 48' and rectifier 49 for providing a reference voltage E-2' between a terminal 42 and grounded conductor 54'. Another transformer 37' and rectifier 38' provide a voltage E-l' between terminal 42 and a terminal 39 that is a function of the magnitude of current in the motor power conductor 23 as previously described. As in the previous instance, a zener diode 56 is connected between terminals 39' and 54' to limit the difference between voltages E-2' and E-l' to a predetermined maximum. Accordingly, a differential voltage 1-3-3 is present across the zener diode 56' and when voltage E-l increases responding portions of the previously described circuit the FIG. 3 circuit is somewhat more susceptible to false counts from brief voltage transients if appropriate corrective measuresare not taken. To guard againstsuch erroneous counts, anti-interference capacitors are'provided at various points in the circuit. This includes capacitors 101 and 102 each connected between'ground and a separate end of the primary'of transforrn'erx48' and a pair of capacitors l03 and '104 similarly connected between opposite ends of the primary of trans former'37' and ground. For similar purposes, still 811.7,.

other pair of capacitors106 and 107 connect between ground and separate ones of the inputs to counter 29'. Considering now the portions of thecircuit 31" which accommodate to a motor work cycle, whic'hkir'icludes two or more current peaks, voltage E-3' is applied to a differentiator circuit 108 of modified form. In partica ular,-one input terminal 109 "of differentiator 108 is connected to the previously described grounded con-- ducto'r 54' while terminal 39 is connected to a terminal 111 of the differentiator through a capacitor 112. A first differentiator resistor. 113 is connected between terminals 109 and 111 while a second resistor 114 is connected between terminal .111 and the DC power terminal 71 When voltage E3- decreases inresponse to an increase of current in motor power conductor 23 as previously described, the differentiating action of I the capacitance and resistance produces a pulse at terminal l11..The pulse is detected by a unij unction'trans sistor 116 which then transmits a setsignal to the input 1170f a flip-flop (bistable multivibrator) circuit 118 to minal 71' through a resistor 119 while'the other base 128' with the 'cmitterfbe'ing connected to iriput; 1 through aresistoi129 and capacitor 131'. Thie;base of, transistor '1 27: is connected toiground through a resistor tional count signals' to counter 29 that their flip-flop 118 is arranged to remain iin the set condition and therefore to be insensitive .to: additional input pulses for a predetermined'period corresponding to a time just a slightly less "than-the period required for'full work cycle of motor 17;

Considering now suitable internal structure for I the flip-flop llfl'whereby thesesresultsl aresaceomplishedaa I a transistor 127 has a collectoriconnected ,to power supply terminal 71 "through a voltagedropping resistor 132 and to the junction between resistor 129 and ca} set the flip-flop. For this purpose, one base electrode of i unijunction transistor 116'is coupled to DC power'ter-,

electrode of the unijunction transistor is coupled to differentiator terminal 109 through a resistor 121. The emitter of unijunction transistor 116 is coupled to the terminal 111 of the differentiator whereby a decrease of voltage E-3 causes the unijunction transistor to become conductive for a brief period. Input 117 of flip flop 118 is connected to the junction between resistor 119 and the unijunction transistor 116 and thus a positive voltage at input 1 17 is momentarily decreased each time transistor 116 conducts.

Flip-flop I 18 has an output conductor 122 connected to ground through a relay driver coil 123 which controls a set of normally open relay contacts 124. A diode pacitor131throughadiodes133andalsotothcoileicz (tor 'of' an additional transistor l34 throiighja resistor I a 136. Thebase'of' trarisistor134 is connected to ground througha resistor'137 andcross, coupled. tq thegqlleg .:=tororrransistemzvnrrdaghregister 138to1p'rovid'e the desired multivibrator action. The ernitterof transistor 134 is connected tog'g r ound'throughresistor 132 and to "the emitter of transistor 127J1 ejcollector'ofitransistor f r I 134 isac'oupled topfiwrsupply tenninalfll'ilthrough a "resistor 141'. The above described cross couplings of the transistors 1'271land 134 result. in. a' bistable action, Y wherein conduction oforie transistor l27f or l3 f4'pre eludes conductionof the other, With transistor 127; initially in a conducting condition, transistor 1534 is biased. 7 into a non-conducting state; Receipt dither-previously describedjset' pulse at input -117v momentarily lowers the base voltage of transistor 127. This cutoff conduc 7 tion through transistor 127.cau'singthe potential atthe: lbaseof transistor'l 34 ilo riisewhereby'ttahsisto'r133 liecomes conductive and thereby holds-transistor 127' in ,the non-conductivestateuntil suchtirne asareset pulse f isfappli'ed to the base ofitransistor 134 r A t thatQtime,

conduction through transistor'l34 is'stopped' and the circuit assumes the origi'nal'stable reset state.

To generate the reset pulseta predetermined time;

after the flipsflop118 is set byaninput pulse, a unijunc tion transistor 143 has an emitter connected to the collector of transistor 127 through a se'lec'tivelyvariable resistance 144 and fixed resistance 146. The emitter'of 7 unijunction transistor 143 is also coupled to ground through a capacitor:l47 which in conjunction with re- 7 sistances 144 and 146 forms'a timedelay circuit of ,se.

126 is'connec'ted across relay driver coil 123 to protect against inverted voltage surges which may accompany deenergization of the coil. As will hereinafter be described in greater detail, closing of the relay contacts 124 supplies a count signal to the counter 29'. In the normal, reset condition of flip-flop 118 output 122 is unenergized and thus relay coil 123 is also unenergized and the contacts 124 remain open. Upon receipt of an input pulse at input 117 as previously described, the flip-flop 118 assumes the alternate condition at which output 122 is energized thereby closing the contacts 124 to transmit a count to counter 29'. In the course of a work cycle of motor 17 this action occurs when the first of a series of major current peaks associated with a work cycle is detected. Subsequent current peaks as sociated with the same work cycle do not produce addilectable timeconstantgwhen transistor 127. turns off in. response to an inputpulse asprevjously described, the

voltage on capacitor 147'begins to rise andreachesa,

potential sufficient to trigger unijunction transistor 143 af er a P i s t me s r in d by. the a ifi s sl; time constantof the R C'network defined by'resistors 144,146and capacitor 147. One base electrode of unijunction transistor'143 is coupled to ground through a resistor'148 while the other base electrode of the unijunction transistor connects to 7 71' through a resistor 149.

- Accordingly the unijuhction' transistor 143 is trig I gered a predetermined interval' aft'er the flip-flop 118 is set thereby producing a reset pulse acrossresistor 14 9. The reset pulse is transmitted to the base of tran- I sistor 134 by a capacitor 151 to turnofi transistor' l34fl and therebycause theflip-flop 118 to revert to the ini tial reset state. a V

The flip-flopllfl controls the relay driver coil 123 in that conductor 122 to the coil is connected to the emitter of a control transistor 152fhavin'g' a collector eon- V power supply terminal 7 nected to the power supply terminal 71.. A resistor 153 is connected between the base of the control transistor 152 and the collector of transistor 127. Thus transistor 152 is held in a nonconductive condition while the flipflop is in the reset condition and becomes conductive to energize relay coil 123 when the flip-flop is set since transistor 127 becomes nonconductive at that time as previously described. To deliver a count signal to counter 29' each time that relay coil 123 is energized, one input to the counter is connected to AC power conductor 33 while the other counter input connects to AC power conductor 34 through relay contacts 124, a resistor 154 and a diode 156. Resistor 154 and diode 156, together with a capacitor 157 act to rectify the count signal voltage transmitted to counter. A capacitor 158 and resistor 159 are connected across relay contacts 124 to suppress arcing at the contacts.

Accordingly, the circuit 31 of FIG. 3 provides for reliable counting of work cycles of motor 17 without regard to number of motor current peaks in the course of a single cycle provided all peaks occur within a predetermined normal work cycle interval.

While the invention has been described with respect to certain preferred embodiments, it will be apparent that many modifications are possible and it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

l. A device for counting work cycles performed by an electrically operated apparatus having conductor means for connection to -a source of electrical power, comprising:

a counter having input means for receiving count signals and having means for recording the number of said count signals received at said input,

current sensing means coupled to said conductor means to sense current changes therein and having means for producing a first continuous voltage which changes in response to said changes of said current,

said source of electrical power, a second full wave rectifier connected'across the secondary winding of said transformer, and an adjustable potentiometer connected across said rectifier.

3. A device as defined in claim 1 wherein said circuit means comprises a Schmitt trigger circuit having an output which changes between a first and a second predetermined fixed electrical states response to said output signals from said comparing means, and means controlled by said output of said Schmitt trigger for transmitting a count signal to said counter upon each change of state of said Schmitt trigger output.

4. A device as defined in claim 1 wherein said circuit means comprises a bistable multivibrator flip-flop circuit having an output which changes state in response to said output signals from said comparing means to assume a set condition, means coupled to said output of said flip-flop for transmitting a count signal to said counter each time said flip-flop assumes said set condition, and means for resetting said flip-flop circuit a predetermined time interval after said flip-flop circuit is set.

5. A'device as defined in claim 1 wherein said means for producing said first voltage has filter means for supressing any significant change of said first voltage when said change of said current is of less duration than a predetermined interval.

6. A device for counting work cycles performed at a machine tool or the like which is driven by an electrical motor having conductors which connect with a source 1 of alternating electrical current and wherein at least voltage sensing means coupled to said conductor means independently of said current sensing means for producing a second continuous voltage which is proportional to the voltage being applied to said apparatus by said source,

means for comparing said first and second voltages for producing an output signal as said first voltage reaches a predetermined relationship to said second voltage, and v circuit means coupled to said comparing means and to said counter input and having means for transmitting count signals to said counter input in response to output signals from said comparing means.

2. A device as defined in claim 1 wherein said current sensing means comprises a first transformer inductively coupled to said conductor means which connects said electrically operated apparatus with said source of electrical power and a first full wave rectifier connected to said transformer to produce said first voltage, and I wherein said voltage sensing means for producing said second voltage comprises 7 a second transformer having primary and secondary windings and having said primary windings connected between a pair of conductors of said conductor means which connects said electrically operated apparatus with one increase of current in said conductors occurs in the course of each work cycle due to increased loading of said motor, comprising:

current sensing transformer means inductively coupled to at least one of said conductors for sensing said current increase therein, variable voltage means including a first rectifier coupled to said transformer means and having a pair of output terminals across which a first continuous voltage is generated which varies in response to said current changes, comparison means connected between a pair of said electrical conductors independently of said transformer means and having a second rectifier and output terminals across which a second continuous voltage is produced which is proportional to the voltage supplied to said motor through said conductors, conductive means interconnecting one output terminal of said variable voltage means with one output terminal of like polarity of said comparison means whereby a third voltage is present between the other terminals of said variable voltage means and said comparison means which third voltage varies in response to said changes of current in said conductors, voltage change detector means coupled between said other terminals of said variable voltage means and said comparison means and having an output for transmitting a signal when said third voltage is reduced to a predetermined value by an increase of said first voltage relative to said second voltage, a counter having input terminals for receiving count signals and having means for recording an accumulated total of said count signals,

relay means connected betvveensaid input terminals of said counter and said source of electrical current,

after a prior-actuation thereof;

8. The combinatior defihed'iiniclaim;further icomal:

prising a breakdown device connected between said other terminals of said variable voltage means andsaid comparison means for limiting said third voltage to a predetermined maximum value. t

9. The combination defined in claim 6 further comprising a differentiator circuit coupling said other terminals and said voltage change detector means. 

1. A device for counting work cycles performed by an electrically operated apparatus having conductor means for connection to a source of electrical power, comprising: a counter having input means for receiving count signals and having means for recording the number of said count signals received at said input, current sensing means coupled to said conductor means to sense current changes therein and having means for producing a first continuous voltage which changes in response to said changes of said current, voltage sensing means coupled to said conductor means independently of said current sensing means for producing a second continuous voltage which is proportional to the voltage being applied to said apparatus by said source, means for comparing said first and second voltages for producing an output signal as said first voltage reaches a predetermined relationship to said second voltage, and circuit means coupled to said comparing means and to said counter input and having means for transmitting count signals to said counter input in response to output signals from said comparing means.
 2. A device as defined in claim 1 wherein said current sensing means comprises a first transformer inductively coupled to said conductor means which connects said eLectrically operated apparatus with said source of electrical power and a first full wave rectifier connected to said transformer to produce said first voltage, and wherein said voltage sensing means for producing said second voltage comprises a second transformer having primary and secondary windings and having said primary windings connected between a pair of conductors of said conductor means which connects said electrically operated apparatus with said source of electrical power, a second full wave rectifier connected across the secondary winding of said transformer, and an adjustable potentiometer connected across said rectifier.
 3. A device as defined in claim 1 wherein said circuit means comprises a Schmitt trigger circuit having an output which changes between a first and a second predetermined fixed electrical states in response to said output signals from said comparing means, and means controlled by said output of said Schmitt trigger for transmitting a count signal to said counter upon each change of state of said Schmitt trigger output.
 4. A device as defined in claim 1 wherein said circuit means comprises a bistable multivibrator flip-flop circuit having an output which changes state in response to said output signals from said comparing means to assume a set condition, means coupled to said output of said flip-flop for transmitting a count signal to said counter each time said flip-flop assumes said set condition, and means for resetting said flip-flop circuit a predetermined time interval after said flip-flop circuit is set.
 5. A device as defined in claim 1 wherein said means for producing said first voltage has filter means for supressing any significant change of said first voltage when said change of said current is of less duration than a predetermined interval.
 6. A device for counting work cycles performed at a machine tool or the like which is driven by an electrical motor having conductors which connect with a source of alternating electrical current and wherein at least one increase of current in said conductors occurs in the course of each work cycle due to increased loading of said motor, comprising: current sensing transformer means inductively coupled to at least one of said conductors for sensing said current increase therein, variable voltage means including a first rectifier coupled to said transformer means and having a pair of output terminals across which a first continuous voltage is generated which varies in response to said current changes, comparison means connected between a pair of said electrical conductors independently of said transformer means and having a second rectifier and output terminals across which a second continuous voltage is produced which is proportional to the voltage supplied to said motor through said conductors, conductive means interconnecting one output terminal of said variable voltage means with one output terminal of like polarity of said comparison means whereby a third voltage is present between the other terminals of said variable voltage means and said comparison means which third voltage varies in response to said changes of current in said conductors, voltage change detector means coupled between said other terminals of said variable voltage means and said comparison means and having an output for transmitting a signal when said third voltage is reduced to a predetermined value by an increase of said first voltage relative to said second voltage, a counter having input terminals for receiving count signals and having means for recording an accumulated total of said count signals, relay means connected between said input terminals of said counter and said source of electrical current for transmitting said count signals to said counter in response to actuation of said relay means, and circuit means for actuating said relay means in response to said output signals from said detector means.
 7. The combination defined in claim 6 whereiN said circuit means has time delay means for blocking reactuation of said relay means for a predetermined interval after a prior actuation thereof.
 8. The combination defined in claim 6 further comprising a breakdown device connected between said other terminals of said variable voltage means and said comparison means for limiting said third voltage to a predetermined maximum value.
 9. The combination defined in claim 6 further comprising a differentiator circuit coupling said other terminals and said voltage change detector means. 